1. Field of the Invention
The present invention relates to a hydrogenation annealing method using a microwave, which performs hydrogenation annealing at a low temperature and with low power in a manufacturing process of a thin film transistor (TFT) for a display device.
2. Background of the Related Art
As a flat display panel, a liquid crystal display (LCD) and an organic light emitting display take a central place.
Requirements in a display market include a low price, a high image quality, a high resolution, and the like and a thin film transistor (TFT) to be applied to a display switching and driving element having excellent performance without increasing cost may be required to meet the requirements.
Therefore, future technological development needs to focus on securing a TFT manufacturing technology that can manufacture a display panel having the excellent performance at the low price with such a trend.
An amorphous silicon thin film transistor (a-Si TFT) generally applied as the display driving and switching element may be uniformly formed on a large substrate with low-price cost, and as a result, the amorphous silicon thin film transistor (a-Si TFT) is a widely used element, but the amorphous silicon thin film transistor (a-Si TFT) reaches the limit with large-size and high-image quality trends.
Therefore, a high-performance TFT and a high-performance technology having higher mobility than the a-Si TFT are required. Further, as the a-Si TFT continuously operates as the maximum disadvantage, an element characteristic continuously deteriorates, and as a result, a problem in reliability in which initial performance cannot be maintained occurs.
This is a primary reason that the a-Si TFT is difficult to apply to an organic luminescence emitted diode (OLED) which operates while continuously making current flow rather than an LCD which is driven with alternating current.
Since a polycrystalline silicon thin film transistor (poly-Si TFT) having even higher performance than the amorphous silicon (a-Si) TFT has high tens to hundreds of mobility, performance which may be applied to a high-definition display which is difficult to implement in the existing a-Si TFT is shown and an element characteristic deterioration problem depending on the operation is very small as compared with the a-Si TFT.
However, more processes are required to manufacture the poly-Si TFT than the a-Si TFT and the resulting additional equipment investment also needs to be preceded.
Therefore, the p-Si TFT is suitable for application to a product such as the high-definition display or the OLED, but smaller than the existing a-Si TFT in terms of the cost, and as a result, the application cannot but be limited.
Accordingly, a request for a new TFT technology which can take both the advantages (large size, low price, and uniformity) of the a-Si TFT and the advantages (high performance and reliability) of the poly-Si TFT is larger than ever and a research thereinto is in active progress and as the representative technology, an oxide semiconductor TFT is provided.
The oxide semiconductor TFT has higher mobility than the amorphous silicon (a-Si) TFT and is simpler in manufacturing process and small in manufacturing cost than the polycrystalline silicon (poly-Si) TFT, and as a result, the oxide semiconductor TFT is high in utility value in the liquid crystal display (LCD) and the organic luminescence emitting diode (OLED).
Meanwhile, an active layer of the oxide semiconductor TFT as a layer forming a channel in which electrons move may be formed by using low temperature poly silicon (LTPS) having higher mobility of the electrons for a high-resolution and 3D flat display in recent years. As a result, an annealing process needs to be added similarly to a process of forming an electrode of an active matrix organic light emitting diode (AMOLED) which is high in response speed, such as a crystallization process, or the like in order to manufacture the LTPS. As an additional process required for the LTPS, the crystallization process and a high-temperature annealing process are provided and the high-temperature annealing process includes a pre-compaction process, a dehydrogenation annealing process, an activation process, and a hydrogenation annealing process.
In the high-temperature annealing process, the hydrogenation annealing process is used for preventing the electrons which pass silicon (Si) on the surface and therein exists as a dangling bond-state active layer are captured at a dangling bonding place and scattering of the electrons from being deteriorated.
When high-temperature annealing is performed through the hydrogenation annealing process, hydrogen atoms are recoupled to the dangling bonding place in which hydrogen is degassed in the crystallization process to enhance the element characteristic.
However, in the hydrogenation annealing process using an induction heating device or a halogen lamp in the related art, there is no effect even though the element is exposed to a comparatively high temperature of 600 to 1000 C temperature for a long time and the process is performed at a temperature of 500° C. or lower. In particular, a long process time is required, which includes a time required to increase a target process temperature, a time when the annealing process is performed at the process temperature, and a time required to decrease the temperature for a subsequent process after the annealing.
As described above, in the hydrogenation annealing process, high power for the annealing is used as the high temperature is required and further, since the element is exposed to the high temperature for a long time, a defect may occur on anther layer constituting the element, and as a result, a yield decreases. Further, a long stand-by time is required to decrease the temperature of the element for the subsequent process of the hydrogenation annealing process and there is a possibility that the element will be deformed while the temperature of the element decreases. In particular, in manufacturing a flexible display, polyimide needs to be annealed at the high temperature after a curing process of polyimide and in this case, a plastic substrate is also deformed or an organic matter is also combusted through combination with oxygen.
Further, the hydrogenation annealing process needs to be performed by increasing the temperature under a high-vacuum atmosphere in order to prevent the annealed element from being contaminated in the related art.